Manitoba Insect Update

July 13, 2009

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives, Crops Knowledge Centre,
Phone: 204-745-5668; Fax: 204-745-5690

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Summary

Levels of barley thrips are of concern in some barley fields in the southwest. Pea aphids are also a concern in the southwest. Grasshoppers are of concern in some areas, particularly in the southwest and central regions.

Recent Insect Concerns and Observations

Barley thrips: There have been several reports of high levels of barley thrips from the southwest region and around Somerset in the central region. Some insecticide applications have been made.
Scouting tips for barley thrips: Most thrips can be found under the top 2 leaf sheaths. A few may be crawling outside the sheath as well. Look on the underside of the sheaths for the thrips. Also check the head if it is developing. Adults are only about 1 to 2 mm long and dark brown or black. Immature stages will be smaller than the adults and white or green, and may be very hard to see on the plant.
One adult thrips per stem on average can result in the loss of about 0.4 bushels per acre. So by knowing the expected value of the barley and expected control costs it should be possible to determine if control would be economical . Growth stage of the barley is also an important consideration. Treatment of barley for barley thrips is only effective if applied before heading is complete.

Grasshoppers: High populations of young grasshoppers continue to be noticed in and around some fields. Most of the reports of higher populations continue to be from the southwest and central regions of Manitoba. If populations are such that it appears control will be needed, grasshoppers are much easier to manage when they are young and concentrated near where they emerged.

Aphids on peas: Flowering is the time when peas should be checked for pea aphids. Pea aphids can be monitored either using a sweep net, or by recording the number per plant tip. If using a sweep net the economic threshold would be 9 to 12 aphids per sweep (90 to 120 aphids if doing 10 sweeps). If counting numbers per plant tip the threshold is about 2-3 aphids per plant tip. If numbers of aphids are at or above the economic threshold, an insecticide application when 50% of plants have produced young pods would be cost effective.


Aphid on pea flower

Surveys and Forecasts

Bertha Armyworm Forecasting: Counts have started to increase in some regions, but still rate as low risk. Highest counts so far are from traps near Miniota (192), Hamiota (137), Elkhorn (124), Belmont (85), and Killarney (81). These still rate as low risk (less than 300), although weekly counts are still increasing and may not have peaked yet. Data can be viewed at:
https://www.gov.mb.ca/agriculture/crops/insects/bertha/index.html

Wheat Midge Emergence: The Canadian Wheat Board produces maps that predict based on growing degree days when wheat midge emergence should be starting and peaking. Maps will be updated daily until the end of July. The maps show that enough degree days have been accumulated for wheat midge to have begun emerging in many areas of southern Manitoba, and emergence may be approaching 50% in southeast Manitoba. Maps can be viewed at: http://www.cwb.ca/public/en/farmers/weather/midge/

Soybean Aphid Monitoring: The following website enables the movement and populations of soybean aphids to be monitored. Although moderate to high levels of soybean aphids have appeared in some areas of Ontario and Quebec, so far there are no reports of soybean aphids from Manitoba. Please contact me if you find or suspect soybean aphids in fields in Manitoba.
http://sba.ipmpipe.org/cgi-bin/sbr/public.cgi?host=All%20Legumes/Kudzu&pest=soybean_aphid